Data storage systems generally store data on physical media, such as direct access hard disks, in a manner that is transparent to host computers. From the perspective of a host computer, data items are stored at logical addresses located on file systems or logical volumes. Data storage systems map the logical addresses to physical locations on the physical media.
A data storage system may implement mechanisms of data redundancy that permit operation to continue if a unit of the physical media fails. Redundancy is achieved by mapping data to physical locations in such a manner that data lost when a unit fails may be retrieved or reconstructed from redundant locations on alternate units. The mapping may be based on methods such as mirroring or a Redundant Array of Inexpensive Disks (RAIDs).
When a unit of storage within a redundant data storage system fails, operation may continue because data stored on the failed unit is accessible elsewhere in the system. If the failed unit is returned to operation, through repair or replacement, the storage system may reconstruct the redundancy of the system by transferring to the returned unit the data stored at the redundant locations. The time delay caused by reconstructing the redundancy is a significant disadvantage of many systems providing redundancy.
A more efficient means of restoring redundant storage units is therefore needed.
Methods are known in the art that predict, or attempt to predict, occurrence of failure or incorrect operation in an element of a storage system. One such method, known as Self-Monitoring Analysis and Reporting Technology (SMART) incorporates logic and/or sensors into a hard disk drive to monitor characteristics of the drive. A more general protocol for monitoring network-connected devices, such as servers and storage systems is Intelligent Platform Management Interface (IPMI). The IPMI specification, developed by Dell, HP, Intel and NEC, defines interfaces for use in monitoring status features such as temperature, voltage, fans, power supplies and chassis. Values of the monitored characteristics are used to predict a possible pending problem, and/or provide an alert for such a problem. A description of IPMI is to be found at www.intel.com/design/servers/ipmi, incorporated herein by reference.